This invention is directed to an air bag gas generator for protecting a passenger from impacts, in particular to an air bag gas generator having a characteristic inner cylindrical member structure contained in a housing.
A conventional air bag gas generator is constructed by forming a housing, having gas discharge ports, by casting, forging, or press work, etc., and providing, inside the housing, an igniting unit, gas generating agents, and a filter unit. Each of these is provided in the housing as is, or the inside of the housing is partitioned by an inner cylindrical member into two or more chambers. Each of the above-mentioned units, respectively, is provided in each of these partitioned chambers, as needed, according to their function.
When the inside of the housing is partitioned by the inner cylindrical member into two or more chambers, the cylindrical member is incorporated into the inner surface of the housing. Specifically, when the housing is formed by casting, the cylindrical member is incorporated into the housing in advance. When forming only the housing by press work, etc., a cylindrical-shaped inner cylindrical member, which is formed separately, is welded onto the inner surface of the ceiling of the housing.
However, when a separately formed inner cylindrical member is attached by welding, etc., to the ceiling portion of the inner surface of the housing, after the housing is formed, these two are welded from an outer surface of the housing. This makes determining the welding point difficult. Especially, when the inner cylindrical member is formed by pressing using a stainless steel sheet, etc., the circumferential wall of the cylindrical member is thin. This makes it more difficult to determine the welding point. If the point where the inner cylindrical member contacts the inner surface of the ceiling portion of the housing and the welding point from the outer surface of the housing are not accurately aligned, even slightly, the two members cannot be reliably attached. Furthermore, if holes are created in both members by welding, while the contact point and welding point are not accurately aligned, neither of these members can be used.
When the inner cylindrical member is joined to the inner surface of the ceiling portion of the housing afterwards, the inner surface of the ceiling portion of the housing ceiling is usually placed on the end surface of the inner cylindrical member and then fixed and secured to a jig. This led to the possibility of unstableness or misalignment (tilting) due to the small contact surface.
Therefore, the present invention resolves the above-mentioned problems by providing an air bag gas generator, in which an inner cylindrical member is welded to the ceiling portion of the inner surface of the housing after the housing is formed, where the inner cylindrical member can be reliably welded to the inner surface of the ceiling portion of the housing even if the welding point is slightly misaligned, and a gas generator having a cylindrical member, which can be welded to a ceiling portion of the inner surface of the housing without causing any instability (a more stable manner) in the area where the cylindrical member abuts the ceiling portion.
The air bag gas generator of the present invention is characterized, in particular, by the shape of the inner cylindrical member contained in the housing. It is further characterized that a broad width area is formed at an end portion of the inner cylindrical member for joining the ceiling of the inner surface.
In other words, the air bag gas generator of the present invention, which is constituted by partitioning the inside of the housing by the inner cylindrical member into two or more chambers, is characterized by the inner cylindrical member having the broad width area, extending inward or outward, at the end portion that joins the inner surface of the ceiling.
The inner cylindrical member can be formed by either casting, forging, or press or cutting work, etc., or a combination of these. When it is formed by press work, it can be formed, for example, by: the UO press method (the sheet is molded into a U shape, then molded into an O shape, and the seam is then welded); the electrical seam tube method (the sheet is molded into a disc shape, and the seam is welded with resistance heat by running a large electrical current while adding pressure to the seam.), etc. When it is formed by cutting work, a stainless steel rod can be cut into a desired size. The broad width portion formed at its end portion is extended to the degree needed to function as the welding area when the inner cylindrical member is welded onto the ceiling of the inner surface of the housing. As a result, the above-mentioned inner cylindrical member and the inner surface of the ceiling of the housing can be reliably joined via the broad width portion. This broad width portion can be, for instance, a flange formed by bending the end portion of the inner cylindrical member, which joins the inner surface of the ceiling of the housing to the outside or inside.
The above-mentioned housing can be formed by casting, forging, press work, etc., and it is preferably formed by welding a diffuser shell having gas discharge ports and a closure shell having an igniting unit storage opening. The two shells can be joined by various welding methods, such as electron-beam welding, laser welding, TIG welding, projection welding, etc. When the housing is formed by welding the diffuser shell and closure shell together, the cylindrical member is welded and incorporated into the inner surface of the circular area of the diffuser shell. The cylindrical member and the diffuser shell can be welded using various welding methods, as in the joining of the above-mentioned two shells. When the diffuser shell and closure shell are formed by press-molding a sheet steel, such as stainless steel sheets, etc., the manufacture of the two shells becomes easy and a reduction in manufacturing cost is achieved. Also, by forming the two shells into simple, cylindrical shapes, the press-molding becomes easy. As for the material for the diffuser shell and closure shell, stainless steel sheet is desirable, but nickel-plated sheet steel may be used.
In the gas generator of the present invention, the inner cylindrical member having the broad width portion is contained in the housing. Aside from this, it has structures and members required for its operation, and structures and members, which are effective for the operation of a gas generator, may also be used as needed. For the structures and members required for operating this gas generator, there are, for instance: an igniting unit, which is activated upon sensing an impact via a mechanical or electrical mechanism; gas generating agents, which are ignited by the activation of the igniting unit and burn and generate combustion gas; a filter unit, which purifies and cools the combustion gas generated; etc. On the other hand, for structures and members that are advantageous for the operation of the gas generator, there are, for instance: a filter support member, which is provided between an inner cylindrical member that partitions to form an igniting unit storage chamber on its inner side and the filter unit, and that which supports the filter unit; a short-pass preventing unit (plate member, etc.), which encloses the top end and/or bottom end of the inner circumference of the filter unit and which prevents the generated gas to pass through a gap between the filter unit and the inner surface of the housing; a cushion member, which is provided above and/or below the gas generating agents to prohibit the gas generating agents from moving; a perforated basket, which has multiple holes, is cylindrical in shape, and it prevents the gas generating agents installed inside of the filter means from directly contacting the filter unit. It also protects the filter unit from the flames from the combustion of the gas generating agents; a space, which is provided between the outer surface of the filter unit and the side wall inner surface of the housing and which functions as a gas channel, etc.
As the method for sensing an impact and method for activating the igniting unit, the air bag gas generator of the present invention can use either a mechanical ignition type, which is activated by sensing an impact exclusively by means of a mechanical method, or an electrical ignition type, which is activated by an electrical signal transmitted from an impact sensor, as long as it uses the inner cylindrical member with the above-mentioned structure.
The mechanical ignition type igniting unit comprises: a mechanical sensor, which senses an impact via an exclusively mechanical method, such as the firing of a firing pin via the movement of a weight, etc.; a detonator, which is ignited when struck by the firing pin fired from the mechanical type sensor and then burns; and a transfer charge, which is ignited by the flame from the detonator and then burns. On the other hand, the electrical ignition type igniting unit comprises: an electrical sensor, which senses an impact exclusively by means of an electrical mechanism; an igniter, which is activated by an electrical signal transmitted from an impact sensor; and a transfer charge, which is ignited by the activation of the igniter and then burns. For the electrical sensor, there are, for instance, a semiconductor type acceleration sensor, etc. This semiconductor-type acceleration sensor has four semiconductor strain gauges formed on a beam of a silicon substrate, which is designed to be deflected when acceleration occurs. These semiconductor strain gauges are bridge connected. When acceleration occurs, the beam is deflected, and the surface is strained. Because of this strain, the resistance of the semiconductor strain gauges changes, and this resistance change is detected as a voltage signal that is proportional to the acceleration. In the electrical ignition type igniting unit, in particular, a control unit with an ignition evaluation circuit may be included. The signal from the above-mentioned semiconductor-type acceleration sensor is inputted in the ignition evaluation circuit; the control unit begins its calculation at the point at which the impact signal exceeds a certain value; and outputs the activation signal to the gas generator when the calculation result exceeds a certain value.
As the above-mentioned gas generating agents, agents based on inorganic azide, which are widely known in the art, in particular a sodium azide, for instance, an equivalent mixture of soda azide and copper oxide, or a non-azide gas generating agent can be used. Various non-azide gas generating agent compositions have been proposed. For example, known compositions are ones primarily composed of an organic compound containing nitrogen, such as tetrazole, triazole, or the metal salts of these, etc., and an oxidizing agent containing oxygen, such as alkali metal nitrate, etc., and compositions using as their fuel and nitrogen source triaminoguanidine nitrate, carbohydrazide, nitroguanizine, etc., and using as their oxidizing agent the nitrate, chlorate, perchlorate, etc., of an alkali metal or alkali earth metal. Any one of these, but certainly not limited to these, may be used as the gas generating agents in this invention, and they are selected as needed according to the burning rate, non-toxicity, and combustion temperature requirements. The gas generating agents are used in the appropriate form such as a pellet, a wafer, a hollow cylinder, multiple holes, a disc, etc.
The filter unit, which is accommodated and installed in the housing, is cylindrical in shape. It functions to remove combustion residues produced by the combustion of the gas generating agents and also to cool the combustion gas. As a filter means, for example, a filter conventionally used for purifying the gas generated in the housing and/or a coolant used for cooling the generated gas are used. Aside from these, a multi-layered wire mesh filter, etc., which has been formed by compression-molding a ring-shaped multi-layered wire mesh, composed of the appropriate material, may also be used. More specifically, the multi-layered wire mesh filter can be formed: by shaping a plain stitch stainless steel wire mesh into a cylindrical body, forming a ring-shaped multi-layered body by repeatedly bending one end of the cylindrical body outward, and compression-molding the multi-layered body in a mold; or shaping plain stitch stainless steel wire mesh into a cylindrical body, forming this into a sheet by pressing this cylindrical body in a radial direction, forming a multi-layered body by multi-rolling this sheet body into a cylindrical shape, and compression-molding this multi-layered body in a mold, etc. The material used for the wire mesh may be stainless steel, such as SUS304, SUS310S, SUS316 (JIS standard code), etc. SUS304 (18Cr-8Ni-0.06C) stainless steel exhibits excellent corrosion resistance as does austenitic stainless steel.
The filter unit can also be of a dual structure having inner or outer layer made of a multi-layered wire mesh body. The inner layer may have a filter unit protection function to protect the filter unit against the flame from the igniting unit bursting toward the filter unit, and protect the filter unit against the high temperature combustion gas or flame of the gas generating agents being ignited by the flame and burning. When the filter unit expands due to the gas pressure when the gas generator is in operation, the outer layer may function as means for preventing expansion of the filter in order to prevent a plenum created between the filter unit and the outer circumferential wall of the housing from being blocked. Incidentally, the expansion of the filter unit can be prohibited by supporting the outer circumference of the filter unit with an outer layer composed of a multi-layered wire mesh body, a perforated cylindrical body, a round belt body, etc.
The above-mentioned air bag gas generator is placed inside a module case along with an air bag that is inflated by introducing the gas generated by the gas generator to constitute an air bag system.
In this air bag system, coupled with the impact sensor sensing an impact, the gas generator is activated and the combustion gas is discharged from the gas discharge ports in the housing. This combustion gas is ejected into the air bag, and because of this, the air bag ruptures the module cover and inflates. The air bag creates a cushion for absorbing the impact between hard structures and a passenger inside a vehicle.
The gas generator of the present invention is formed using an inner cylindrical member with the above-mentioned broad width portion; thus, it is possible to assimilate a welding point/beam misalignment. Moreover, the inner cylindrical member can be completely secured without creating any gap or tilt at the contact area with the bottom surface portion of the diffuser, resulting in a gas generator for an air bag in which the inner surface of the ceiling portion of the housing is reliably attached with the end portion of the inner cylindrical member.